hdu1242 Rescue （dfs+剪枝）

Problem Description

Angel was caught by the MOLIGPY! He was put in prison by Moligpy. The prison is described as a N * M (N, M <= 200) matrix. There are WALLs, ROADs, and GUARDs in the prison.

Angel’s friends want to save Angel. Their task is: approach Angel. We assume that “approach Angel” is to get to the position where Angel stays. When there’s a guard in the grid, we must kill him (or her?) to move into the grid. We assume that we moving up, down, right, left takes us 1 unit time, and killing a guard takes 1 unit time, too. And we are strong enough to kill all the guards.

You have to calculate the minimal time to approach Angel. (We can move only UP, DOWN, LEFT and RIGHT, to the neighbor grid within bound, of course.)

Input

First line contains two integers stand for N and M.

Then N lines follows, every line has M characters. “.” stands for road, “a” stands for Angel, and “r” stands for each of Angel’s friend.

Process to the end of the file.

Output

For each test case, your program should output a single integer, standing for the minimal time needed. If such a number does no exist, you should output a line containing “Poor ANGEL has to stay in the prison all his life.”

Sample Input

7 8

#.#####.

#.a#..r.

#..#x…

..#..#.#

#…##..

.#……

……..

Sample Output

13

思路

注意Angle朋友不止一个.

/*************************************************************************
> File Name: hdu1242.cpp
> Author:gens_ukiy
> Mail:
> Created Time: 2016年12月02日 星期五 14时53分46秒
************************************************************************/

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<climits>
#include<string>
#include<cstring>
#include<vector>
#include<set>
#include<list>
#include<map>
int dire[4][2]={ {0,1},{1,0},{0,-1},{-1,0} };
int dire2[8][2]={{-1,-1},{-1,0},{-1,1},{ 0,-1},{ 0,1},{ 1,-1},{ 1,0},{ 1,1}};
#define rep(i,a,b) for(int i=(a);i<=(b);(i++))
#define inf 0x3f3f3f
#define ll long long
#define pi acos(-1)
using namespace std;

char a[205][205];
int n,m;
int tot;
int sx,sy;
void dfs(int x,int y,int step){
int flag=0;
if(x<1||x>n||y<1||y>m) return;
if(a[x][y]=='#') return;
if(step>tot) return;
if(a[x][y]=='x'){
step++;
flag=1;
}

if(a[x][y]=='r'){
tot=tot>step?step:tot;
return;
}
rep(i,0,3){
int px=x+dire[i][0];
int py=y+dire[i][1];
a[x][y]='#';
dfs(px,py,step+1);
if(flag==1) a[x][y]='x';
else a[x][y]='.';
}

}

int main()
{
#ifndef OnlineJudge
//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);
#endif
while(cin>>n>>m){

tot=inf;
rep(i,1,n){
scanf("%s",a[i]+1);
rep(j,1,m)
if(a[i][j]=='a')
sx=i,sy=j;
}
dfs(sx,sy,0);
if(tot==inf)
printf("Poor ANGEL has to stay in the prison all his life.\n");
else
printf("%d\n",tot);
}
return 0;
}